An acceleration device is known in the art, according to which the acceleration device is mounted in a vehicle so that a vehicle driving condition is controlled depending on a pedal stroke operated by a vehicle driver. In such a conventional acceleration device, an acceleration pedal is rotatably supported by a supporting member, which is fixed to a vehicle body. The acceleration pedal is rotated in a forward direction by the operation of the vehicle driver and rotated in a reverse direction by a reactive force of a double coil spring when driver's stepping force is released from the acceleration pedal.
According to an acceleration device, for example, as disclosed in Japanese Patent Publication No. 2007-113525, a spring damper, which is made of elastic material and formed in a cross shape, is disposed in an annular space formed between an outer coil spring and an inner coil spring of a double coil spring. The spring damper attenuates vibrations of the outer and inner coil springs so as to suppress generation of abnormal noise resulting from the vibrations.
According to the spring damper of this kind, however, there is a concern that a forward end of the cross-shaped spring damper may be easily inserted into a longitudinal gap of spring wires of the outer coil spring and may outwardly protrude when the double coil spring is expanded. When the forward end of the spring damper, which has outwardly protruded from the outer coil spring through the longitudinal gap, is compressed between the neighboring spring wires during the compression of the double coil spring, it may become difficult for the spring damper to sufficiently attenuate the vibrations of the outer and inner coil springs.
The double coil spring has the outer and inner coil springs, diameters of which are different from each other depending on characteristic of pedal stepping force for the acceleration device to be mounted on various types of vehicles. Therefore, the annular space formed between the outer and inner coil springs varies depending on a combination of the outer and inner coil springs. It is difficult for the cross-shaped spring damper to surely push both of the outer and inner coil springs to thereby attenuate the vibrations thereof, when one type of the cross-shaped spring damper is applied to various types of the double coil springs having different annular spaces between the outer and inner coil springs.